Melatonin promotes reduction in TNF levels and improves the lipid profile and insulin sensitivity in pinealectomized rats with periodontal disease

Prospective and challenges of locally applied repurposed pharmaceuticals for periodontal tissue regeneration

Periodontitis is a persistent inflammatory condition that causes periodontal ligament degradation, periodontal pocket development, and alveolar bone destruction, all of which lead to the breakdown of the teeth's supporting system. Periodontitis is triggered by the accumulation of various microflora (especially anaerobes) in the pockets, which release toxic substances and digestive enzymes and stimulate the immune system. Periodontitis can be efficiently treated using a variety of techniques, both regional and systemic. Effective therapy is dependent on lowering microbial biofilm, minimizing or eradicating pockets. Nowadays, using local drug delivery systems (LDDSs) as an adjuvant therapy to phase I periodontal therapy is an attractive option since it controls drug release, resulting in improved efficacy and lesser adverse reactions. Choosing the right bioactive agent and mode of delivery is the foundation of an efficient periodontal disease management approach. The objective of this paper is to shed light on the issue of successful periodontal regeneration, the drawbacks of currently implemented interventions, and describe the potential of locally delivered repurposed drugs in periodontal tissue regeneration. Because of the multiple etiology of periodontitis, patients must get customized treatment with the primary goal of infection control. Yet, it is not always successful to replace the lost tissues, and it becomes more challenging as the defect gets worse. Pharmaceutical repurposing offers a viable, economical, and safe alternative for non-invasive, and predictable periodontal regeneration. This article clears the way in front of researchers, decision-makers, and pharmaceutical companies to explore the potential, effectiveness, and efficiency of the repurposed pharmaceuticals to generate more economical, effective, and safe topical pharmaceutical preparations for periodontal tissue regeneration.

Therapeutic applications of melatonin in disorders related to the gastrointestinal tract and control of appetite

Most animals have large amounts of the special substance melatonin, which is controlled by the light/dark cycle in the suprachiasmatic nucleus. According to what is now understood, the gastrointestinal tract (GIT) and other areas of the body are sites of melatonin production. According to recent studies, the GIT and adjacent organs depend critically on a massive amount of melatonin. Not unexpectedly, melatonin's many biological properties, such as its antioxidant, anti-inflammatory, pro-apoptotic, anti-proliferative, anti-metastasis, and antiangiogenic properties, have drawn the attention of researchers more and more. Because melatonin is an antioxidant, it produces a lot of secretions in the GIT's mucus and saliva, which shields cells from damage and promotes the development of certain GIT-related disorders. Melatonin's ability to alter cellular behavior in the GIT and other associated organs, such as the liver and pancreas, is another way that it functions. This behavior alters the secretory and metabolic activities of these cells. In this review, we attempted to shed fresh light on the many roles that melatonin plays in the various regions of the gastrointestinal tract by focusing on its activities for the first time.

Role of Melatonin in the Onset of Metabolic Syndrome in Women

Metabolic syndrome (MetS) is a constellation of several associated cardiometabolic risk factors that increase the risk of developing type 2 diabetes mellitus (T2DM), cardiovascular diseases, and mortality. The role of hormonal factors in the development of MetS is assumed. In women, an insulin-resistant state that is associated with polycystic ovarian syndrome and increased deposition of intra-abdominal adipose tissue promotes the development of MetS and increases cardiovascular risk. The neuroendocrine hormone melatonin is secreted mainly at night under the regulatory action of the suprachiasmatic nucleus in the hypothalamus. Melatonin secretion is influenced by exogenous factors such as light and seasons and endogenous factors such as age, sex, and body weight. At present, the role of melatonin in metabolic disorders in humans is not fully understood. In this review, we set out to analyze the relationship of melatonin with the main features of MetS in women. Data from experimental and clinical studies on the role of melatonin in glucose metabolism and on the involvement of melatonin in lipid disturbances in MetS are reviewed. The complex influence of melatonin on hypertension is discussed. The changes in melatonin, leptin, and ghrelin and their relation to various metabolic processes and vascular dysfunction are discussed.

Melatonin decreases plasma TNF-α and improves nonenzymatic antioxidant defence and insulin sensitivity in rats with apical periodontitis fed a high-fat diet

AIM

To analyse the effects of melatonin (ME) treatment on oxidative stress and insulin resistance (IR) in rats with apical periodontitis (AP) fed a high-fat diet (HFD).

METHODOLOGY

Eighty 60-day-old rats were divided into eight groups: control (CN), AP, HFD with AP (HFDAP), control with ME (CNME), AP with ME (APME), HFD with ME (HFDME) and HFD with AP+ME (HFDAPME). The animals from the HFD groups were fed a HFD throughout the experimental period. On day 7, the animals from the AP groups were subjected to experimental AP, and after 70 days, the ME groups were treated for 30 days. Glycaemia, insulinaemia, homeostatic model assessment for IR index, tumour necrosis factor-α (TNF-α), and interleukin-6 were analysed in plasma using biochemical tests and enzyme-linked immunosorbent assay. Thiobarbituric acid-reactive substances (TBARS), carbonyl protein (CP), superoxide dismutase (SOD), catalase, glutathione peroxidase, glutathione (GSH) and total antioxidant capacity (ferric reducing antioxidant power [FRAP]) were analysed in the gastrocnemius muscle.

RESULTS

(1) Association of AP and HDF exacerbated IR, and ME treatment improved this alteration; (2) AP and HFD and their association showed increased TNF-α, and ME reversed it; (3) TBARS increased in the AP and HFDAP groups, and ME reversed only in the group with the association of disease and diet; (4) CP increased in all HFD groups and improved in the ME groups; (5) GSH activity decreased in all experimental groups, and ME increased this parameter only in the CN and AP groups; (6) FRAP did not change between the groups, but ME treatment increased its activity in the AP and HFD groups; (7) ME increased SOD in the CN and AP groups.

CONCLUSION

Apical periodontitis and HFD promoted IR, and the association of AP with diet promoted IR exacerbation; this resistance might have been caused by an increase in TNF-α. AP promoted more intense changes in lipid oxidative damage than in protein oxidative damage. In non-enzymatic antioxidant defence, it was observed that both AP and HFD and their association promoted a decrease in GSH levels. Overall, ME treatment reversed changes such as oxidative stress and IR.

Melatonin decreases IRF-3 protein expression in the gastrocnemius muscle, reduces IL-1β and LPS plasma concentrations, and improves the lipid profile in rats with apical periodontitis fed on a high-fat diet

To evaluate the effects of melatonin (MEL) on the expression of toll-like receptor-4 (TLR4); myeloid differentiation primary response protein-88 (MyD88); TIR-domain-containing adapter-inducing interferon-β (TRIF); IFN regulatory-factor-3 (IRF-3); nuclear factor kappa-B (NF-κB); plasma concentrations of interleukin-1β (IL-1β) and lipopolysaccharide (LPS); and lipid profile of rats with apical periodontitis (AP) fed on a high-fat diet (HFD). Eighty 60-day-old rats were divided into eight groups: control, AP, HFD, HFDAP, CNMEL, APMEL, HFDMEL and HFDAPMEL. HFD groups were fed on a HFD for 107 days. On day 7, experimental AP was induced in the AP groups, and after 70 days, MEL (5 mg/kg) was administered to the MEL groups for 30 days. Plasma concentrations of LPS and IL-1β were analyzed using enzyme-linked immunosorbent assay, and the lipid profile was analyzed using biochemical tests. The expression of proteins involved in the TLR4 pathway (TLR4, MyD88, TRIF, IRF-3 and NF-κB) in the gastrocnemius muscle (GM) was evaluated using western blotting and qRT-PCR. Treatment with MEL decreased IRF-3 protein expression in GM and IL-1β plasma concentration in the APMEL and HFDMEL groups. Reduction in LPS plasma concentration was reported only in the HFDMEL group. Additionally, a decrease in LDL and an increase in HDL were observed in the HFDMEL and HFDAPMEL groups. Treatment with MEL exhibited anti-inflammatory and anti-hyperlipidemic effects attributed to HFD and AP by reducing the plasma concentrations of IL-1β and LPS in addition to reducing IRF-3 protein expression in the GM, which is associated with the production of inflammatory cytokines.

Beneficial Effects of Melatonin on Periodontitis Management: Far More Than Oral Cavity

Periodontitis as a highly prevalent chronic infection/inflammatory disease can eventually lead to tooth loss and masticatory dysfunction. It also has a negative impact on general health and largely impairs quality of life. The tissue destruction during periodontitis is mainly caused by the excessive immune-inflammatory response; hence, how to modulate the host's reaction is of profound importance for effective periodontal treatment and tissue protection. Melatonin, as an endogenous hormone exhibiting multiple biological functions such as circadian rhythm regulation, antioxidant, and anti-inflammation, has been widely used in general healthcare. Notably, the past few years have witnessed increasing evidence for the application of melatonin as an adjunctive approach in the treatment of periodontitis and periodontitis-related systemic comorbidities. The detailed underlying mechanisms and more verification from clinical practice are still lacking, however, and further investigations are highly required. Importantly, it is essential to establish standard guidelines in the near future for the clinical administration of melatonin for periodontal health and general wellbeing.

Locally Applied Repositioned Hormones for Oral Bone and Periodontal Tissue Engineering: A Narrative Review

Bone and periodontium are tissues that have a unique capacity to repair from harm. However, replacing or regrowing missing tissues is not always effective, and it becomes more difficult as the defect grows larger. Because of aging and the increased prevalence of debilitating disorders such as diabetes, there is a considerable increase in demand for orthopedic and periodontal surgical operations, and successful techniques for tissue regeneration are still required. Even with significant limitations, such as quantity and the need for a donor area, autogenous bone grafts remain the best solution. Topical administration methods integrate osteoconductive biomaterial and osteoinductive chemicals as hormones as alternative options. This is a promising method for removing the need for autogenous bone transplantation. Furthermore, despite enormous investigation, there is currently no single approach that can reproduce all the physiologic activities of autogenous bone transplants. The localized bioengineering technique uses biomaterials to administer different hormones to capitalize on the host’s regeneration capacity and capability, as well as resemble intrinsic therapy. The current study adds to the comprehension of the principle of hormone redirection and its local administration in both bone and periodontal tissue engineering.

Melatonin and melatonin-agonists for metabolic syndrome components in patients treated with antipsychotics: A systematic review and meta-analysis

OBJECTIVE

Metabolic side effects are a limiting factor in the use of antipsychotics, which remain the cornerstone of long-term management of patients with severe mental illness. There is contrasting evidence on a possible role of melatonin and melatonin-agonists in attenuating antipsychotic-induced metabolic abnormalities.

DESIGN

We conducted a systematic review (PubMed, PsycInfo, Cochrane databases, up to August 2020) and a random-effect meta-analysis of double-blind, randomized placebo-controlled trials (RCTs) involving melatonin and melatonin-agonists in the treatment of antipsychotic-induced metabolic changes. The primary outcome was the standardized mean difference (SMD) of composite metabolic outcomes built with metabolic syndrome components. Secondary outcomes were individual metabolic syndrome components, and other anthropometric, glucose metabolism, lipid profile, and psychopathology measures.

RESULTS

Out of the initial 41 studies, six documented five separate RCTs randomizing 248 patients (126 to melatonin/ramelteon, 122 to placebo) affected by schizophrenia-spectrum disorders and bipolar disorder. Melatonin/ramelteon outperformed placebo on the primary outcome (SMD -0.28, 95% CI = -0.39 ÷ -0.168), as well as on all individual components of metabolic syndrome (systolic blood pressure MD -3.266, 95% CI = -6.020 ÷ -0.511; fasting glucose MD -3.766, 95% CI = -5.938 ÷ -1.593; triglycerides MD -9.800, 95% CI = -19.431 ÷ -0.169; HDL MD 2.995, 95% CI = 0.567 ÷ 5.423), except waist circumference.

CONCLUSIONS

Melatonin/ramelteon augmentation may be beneficial for non-anthropometric metabolic syndrome components in patients treated with antipsychotics.

Melatonin-doped polymeric nanoparticles induce high crystalline apatite formation in root dentin

OBJECTIVE

To investigate the effect of novel polymeric nanoparticles (NPs) doped with melatonin (ML) on nano-hardness, crystallinity and ultrastructure of the formed hydroxyapatite after endodontic treatment.

METHODS

Undoped-NPs and ML-doped NPs (ML-NPs) were tested at radicular dentin, after 24 h and 6 m. A control group without NPs was included. Radicular cervical and apical dentin surfaces were studied by nano-hardness measurements, X-ray diffraction and transmission electron microscopy. Mean and standard deviation were analyzed by ANOVA and Student-Newman-Keuls multiple comparisons (p < 0.05).

RESULTS

Cervical dentin treated with undoped NPs maintained its nano-hardness values after 6 m of storage being [24 h: 0.29 (0.01); 6 m: 0.30 (0.02) GPa], but it decreased at apical dentin [24 h: 0.36 (0.01); 6 m: 0.28 (0.02) GPa]. When ML-NPs were used, nano-hardness was similar over time [24h: 0.31 (0.02); 6 m: 0.28 (0.03) GPa], at apical dentin. Root dentin treated with ML-NPs produced, in general, high crystallinity of new minerals and thicker crystals than those produced in the rest of the groups. After 6 m, crystals became organized in randomly oriented polyhedral, square polygonal block-like apatite or drop-like apatite polycrystalline lattices when ML-NPs were used. Undoped NPs generated poor crystallinity, with preferred orientation of small crystallite and increased microstrain.

SIGNIFICANCE

New polycrystalline formations encountered in dentin treated with ML-NPs may produce structural dentin stability and high mechanical performance at the root. The decrease of mechanical properties over time in dentin treated without NPs indicates scarce remineralization potential, dentin demineralization and further potential degradation. The amorphous stage may provide high hydroxyapatite solubility and remineralizing activity.

Melatonin-doped polymeric nanoparticles reinforce and remineralize radicular dentin: Morpho-histological, chemical and biomechanical studies

OBJECTIVES

To investigate the effectiveness of novel polymeric nanoparticles (NPs) doped with melatonin (ML) in reducing dentin permeability and facilitating dentin remineralization after endodontic treatment.

METHODS

The effect of undoped NPs and ML-doped NPs (ML-NPs) was tested in radicular dentin, at 24 h and 6 m. A control group without NPs was included. ML liberation was measured. Radicular dentin was assessed for fluid filtration. Dentin remineralization was analyzed by scanning electron microscopy, AFM, Young's modulus (Ei), Nano DMA-tan delta, and Raman analysis.

RESULTS

ML release ranged from 1.85 mg/mL at 24 h to 0.033 mg/mL at 28 d. Both undoped NPs and ML-NPs treated dentin exhibited the lowest microleakage, but samples treated with ML-NPs exhibited hermetically sealed dentinal tubules and extended mineral deposits onto dentin. ML-NPs promoted higher and durable Ei, and functional remineralization at root dentin, generating differences between the values of tan delta among groups and creating zones of stress concentration. Undoped-NPs produced closure of some tubules and porosities at the expense of a relative mineral amorphization. Chemical remineralization based on mineral and organic assessments was higher in samples treated with ML-NPs. When using undoped NPs, precipitation of minerals occurred; however, radicular dentin was not mechanically reinforced but weakened over time.

SIGNIFICANCE

Application of ML-NPs in endodontically treated teeth, previous to the canal filling step, is encouraged due to occlusion of dentinal tubules and the reinforcement of the radicular dentin structure.

Insight into the roles of melatonin in bone tissue and bone‑related diseases (Review)

Bone‑related diseases comprise a large group of common diseases, including fractures, osteoporosis and osteoarthritis (OA), which affect a large number of individuals, particularly the elderly. The progressive destruction and loss of alveolar bone caused by periodontitis is a specific type of bone loss, which has a high incidence and markedly reduces the quality of life of patients. With the existing methods of prevention and treatment, the incidence and mortality of bone‑related diseases are still gradually increasing, creating a significant financial burden to societies worldwide. To prevent the occurrence of bone‑related diseases, delay their progression or reverse the injuries they cause, new alternative or complementary treatments need to be developed. Melatonin exerts numerous physiological effects, including inducing anti‑inflammatory and antioxidative functions, resetting circadian rhythms and promoting wound healing and tissue regeneration. Melatonin also participates in the health management of bone and cartilage. In the present review, the potential roles of melatonin in the pathogenesis and progression of bone injury, osteoporosis, OA and periodontitis are summarized. Furthermore, the high efficiency and diversity of the physiological regulatory effects of melatonin are highlighted and the potential benefits of the use of melatonin for the clinical prevention and treatment of bone‑related diseases are discussed.

Potential Role of Melatonin as an Adjuvant for Atherosclerotic Carotid Arterial Stenosis

Carotid artery stenosis (CAS) is an atherosclerotic disease characterized by a narrowing of the artery lumen and a high risk of ischemic stroke. Risk factors of atherosclerosis, including smoking, hypertension, hyperglycemia, hyperlipidemia, aging, and disrupted circadian rhythm, may potentiate atherosclerosis in the carotid artery and further reduce the arterial lumen. Ischemic stroke due to severe CAS and cerebral ischemic/reperfusion (I/R) injury after the revascularization of CAS also adversely affect clinical outcomes. Melatonin is a pluripotent agent with potent anti-inflammatory, anti-oxidative, and neuroprotective properties. Although there is a shortage of direct clinical evidence demonstrating the benefits of melatonin in CAS patients, previous studies have shown that melatonin may be beneficial for patients with CAS in terms of reducing endothelial damage, stabilizing arterial plaque, mitigating the harm from CAS-related ischemic stroke and cerebral I/R injury, and alleviating the adverse effects of the related risk factors. Additional pre-clinical and clinical are required to confirm this speculation.

Effects of melatonin on insulin signaling and inflammatory pathways of rats with apical periodontitis

AIM

To verify the effects of melatonin supplementation on insulin sensitivity, plasma concentrations of inflammatory cytokines, insulin signalling and inflammatory pathways in the soleus (SM) and extensor digitorum longus (EDL) muscles of rats with apical periodontitis (AP).

METHODOLOGY

Seventy-two Wistar rats were distributed into 4 groups: (a) control (C), (b) control supplemented with melatonin (M), (c) AP (AP), and (d) AP supplemented with melatonin (AP + M). AP was induced by pulp exposure of the maxillary and mandibular right first and second molars to the oral environment. After AP induction, oral supplementation with 5 mg kg^-1 melatonin (diluted in drinking water) for 60 days was initiated. At the end of the treatment, the following were analysed: (1) plasma concentrations of insulin and inflammatory cytokines (TNF-α, IL-6, IL-1β and IL-10) using ELISA kits; (2) glycaemia using enzymatic assay; (3) insulin resistance using homoeostasis model assessment of insulin resistance (HOMA-IR) index; and (4) phosphorylation status of pp185 tyrosine, Akt serine, IKKα/β, and JNK in SM and EDL using Western blot. Analysis of variance of two or three factors was performed, followed by the Bonferroni test. P values < 0.05 were considered statistically significant.

RESULTS

AP promoted insulin resistance, significantly increased (P < 0.05) plasma concentrations of pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β), significantly decreased (P < 0.05) the concentration of anti-inflammatory cytokine IL-10, impaired insulin signalling in SM, and increased IKKα/β phosphorylation status in SM and EDL. Melatonin supplementation in rats with AP improved insulin sensitivity, significantly decreased (P < 0.05) TNF-α and IL-1β, significantly increased (P < 0.05) IL-10 plasma concentrations, and changed the insulin signalling in soleus muscle and IKKα/β phosphorylation status in SM and EDL muscles.

CONCLUSIONS

Melatonin is a potent adjuvant treatment for improving apical periodontitis-associated changes in insulin sensitivity, insulin signalling and inflammatory pathways. In addition, the negative impact of AP on general health was also demonstrated.

Melatonin regulates Aβ production/clearance balance and Aβ neurotoxicity: A potential therapeutic molecule for Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disease with multiple predisposing factors and complicated pathogenesis. Aβ peptide is one of the most important pathogenic factors in the etiology of AD. Accumulating evidence indicates that the imbalance of Aβ production and Aβ clearance in the brain of AD patients leads to Aβ deposition and neurotoxic Aβ oligomer formation. Melatonin shows a potent neuroprotective effect and can prevent or slow down the progression of AD, supporting the view that melatonin is a potential therapeutic molecule for AD. Melatonin modulates the regulatory network of secretase expression and affects the function of secretase, thereby inhibiting amyloidogenic APP processing and Aβ production. Additionally, melatonin ameliorates Aβ-induced neurotoxicity and probably promotes Aβ clearance through glymphatic-lymphatic drainage, BBB transportation and degradation pathways. In this review, we summarize and discuss the role of melatonin against Aβ-dependent AD pathogenesis. We explore the potential cellular and molecular mechanisms of melatonin on Aβ production and assembly, Aβ clearance, Aβ neurotoxicity and circadian cycle disruption. We summarize multiple clinical trials of melatonin treatment in AD patients, showing that melatonin has a promising effect on improving sleep quality and cognitive function. This review aims to stimulate further research on melatonin as a potential therapeutic agent for AD.

Pineal gland protects against chemically induced oral carcinogenesis and inhibits tumor progression in rats

Clinical investigations suggest that melatonin suppression and circadian dysfunction may be related to cancer development in shift workers. Studies also show that melatonin suppression after pinealectomy increases cancer incidence in preclinical models. However, no study evaluated the influence of pinealectomy on oral cancer development. In the current study, we investigated the effects of pinealectomy on oral squamous cell carcinoma (OSCC) occurrence and progression in rats. Rats submitted to sham surgery were used as control. Pinealectomy promoted an increase of 140% in OSCC occurrence when compared to sham animals. Tumors from pinealectomized rats displayed a higher volume and thickness than the tumors from sham-operated animals. Pinealectomy induced atrophy of the epithelium adjacent to the oral lesions. Pinealectomized rats showed higher mean number of tumor-associated macrophages and eosinophils in the invasive front of OSCC. In addition, nuclear overexpression of ERK1/2 and p53 was also observed in the front of carcinomas from pinealectomized rats. These results reveal that pineal gland plays a protective role against oral carcinogenesis. The melatonin suppression caused by the pinealectomy might contribute to oral cancer development by acting on ERK1/2 and p53 pathways and regulating tumor inflammation.

Melatonin alleviates cognition impairment by antagonizing brain insulin resistance in aged rats fed a high-fat diet

Brain insulin resistance, induced by neuroinflammation and oxidative stress, contributes to neurodegeneration, that is, processes that are associated with Aβ accumulation and TAU hyperphosphorylation. Here, we tested the effect of chronic administration of melatonin (MLT) on brain insulin resistance and cognition deficits caused by a high-fat diet (HFD) in aged rats. Results showed that MLT supplementation attenuated peripheral insulin resistance and lowered hippocampal oxidative stress levels. Activated microglia and astrocytes and hippocampal levels of TNF-α in HFD-fed rats were reduced by MLT treatment. Melatonin also prevented HFD-induced increases in beta-amyloid (Aβ) accumulation and TAU phosphorylation in the hippocampus. In addition, impairments of brain insulin signaling elicited by long-term HFD were restored by MLT treatment, as confirmed by ex vivo insulin stimulation. Importantly, MLT reversed HFD-induced cognitive decline as measured by a water maze test, normalized hippocampal LTP and restored CREB activity and BDNF levels as well as cholinergic neuronal activity in the hippocampus. Collectively, these findings indicate that MLT may exhibit substantial protective effects on cognition, via restoration of brain insulin signaling.

The Mystery behind the Pineal Gland: Melatonin Affects the Metabolism of Cholesterol

Melatonin may be considered a cardioprotective agent. Since atherogenesis is partly associated with the metabolism of lipoproteins, it seems plausible that melatonin affects cardiovascular risk by modulating the metabolism of cholesterol and its subfractions. Moreover, cholesterol-driven atherogenesis can be hypothetically reduced by melatonin, mainly due to the minimalization of harmful reactions triggered in the cardiovascular system by the reactive oxygen species-induced toxic derivatives of cholesterol. In this review, we attempted to summarize the available data on the hypolipemizing effects of melatonin, with some emphasis on the molecular mechanisms underlying these reactions. We aimed to attract readers' attention to the numerous gaps of knowledge present in the reviewed field and the essential irrelevance between the findings originating from different sources: clinical observations and in vitro mechanistic and molecular studies, as well as preclinical experiments involving animal models. Overall, such inconsistencies make it currently impossible to give a reliable opinion on the action of melatonin on the metabolism of lipoproteins.